1. Field of the Invention.
This invention relates to the field of textile technology and in particular to the formation of bobbins (usually termed "cops") wherein threads and yarns are wound, usually on yarn drawing-twisting machines, about a tubular body, namely a metal tube coated with a thermoplastic resin, the bobbin having on one tube end thereof previously formed yarn coils projecting out of the yarn winding and forming a so called "transferring tail."
More specifically, this invention relates to a method and a device for securing the end of the transferring tail to the bobbin tube, in such a manner that such end be firmly retained after the bobbin or cop is removed from the winding spindle and stored, conveyed or manipulated, until its thread or yarn is used. The method and device according to this invention are particularly significant and interesting when a wholly automatic production cycle is followed, and specifically when the winding equipment comprises automatic devices to take-off and transport the wound cops without any manual intervention.
2. Description of the Prior Art.
Since in such cases the operations of wound bobbin removal, cutting or tearing-off the yarn at the end of the transferring tail and securing the tail end to a tube free portion cannot be manually performed, different methods have been proposed in order to prearrange the tube for tail end securing and yarn tearing-off, due to the same cop withdrawal and removal motion. The most widely known methods comprise the previous application of a flexible tongue or tab to one tube end, a portion of the tongue being caused to adhesively adhere to the tube surface, while a not adhering tongue portion is slightly lifted from the surface to allow the transferring tail end to become engaged thereunder and against the tube surface, in a sufficiently firm manner to ensure a resistance allowing the yarn to be torn off directly beyond the securing or engaging point, during the cop removal, while retaining the tail end in place. However, the tongue or tab (usually made of a suitably strong and resilient paper, plastics or the like) should be easily removable by hand, for subsequent yarn utilization, without appreciably damaging the tube coating surface.
As is well known, many limitations and drawbacks are encountered in using such systems. One of such limitations is due to the fact that the tongue adhesion should meet the conflicting requirements to ensure a firm yarn adhesion or securing when in use, and simultaneously to make easy the removal thereof. A further drawback consists in that, particularly in case of a relatively slow removal of the wound cop from the spindle, a tongue delamination and detachment action is exerted by the yarn progressively engaging thereunder and at the interface between the tongue and tube surface.
However, probably the greatest drawback of these known systems consists in that the tongue or tab, as previously applied to the tube, should maintain itself in place, under the conditions as required for a ready engagement of the yarn below its free or not adhesively connected portion, during the entire time (that may amount even to many hours) required for the completion of winding, while the tube is driven at a very high speed, of the order of many thousands RPM (i.e. at the speed of modern winding frames). Under the combined action of the very high rotary speed and of the resistance encountered by the tongue contacting air, the tongue is bent outwardly and sometimes its free end portion extends opposite to the direction required for yarn engagement. Such drawback may be at least partly avoided by winding a few yarn turns (which will not form the transferring tail) about the tongue. However, this results in another heavy drawback, in that due to the fact that the tongue is then kept firmly pressed across its whole length against the surface of the tube, the free portion of the tongue cannot in that separate into the spread apart position required to ensure a ready engagement of the yarn thereunder. Even with tongues of a particularly strong material, having a quick elastic reaction and a particular shape of their contour (i.e. highly expensive and not easily applied tongues), the known systems fail to ensure that no operational problems are encountered, with a consequent failure to secure the transfer tail. Obviously, the above represents a heavy drawback particularly in wholly automatized plants, since it leads to rejects, to the necessity of testing each wound cop, and so on.
Complementarily, a number of drawbacks also arise when using adhesives for initially securing the tongue to the tube surface. Thus, e.g., a given setting time is required by such adhesives to ensure a firm connection. Further, adhesive degradation may occur under the combined action of centrifugal force and ventilation, with the consequent decrease or even annulment of strength of the adhesive. Generally speaking, the adhesives are not very suitable for use on plastics surfaces, and when a physical-chemical attack is used to ensure the required bond, the subsequent tearing-off of the tongue results in an inadmissible damage to the plastics tube surface.